ADS8320E Burr-Brown Corporation, ADS8320E Datasheet - Page 9

• Manufacturer Part Number: ADS8320E
• Description: 16-Bit/ High-Speed/ 2.7V to 5V microPower Sampling ANALOG-TO-DIGITAL CONVERTER
• Manufacturer: Burr-Brown Corporation

FIGURE 1. Histogram of 5000 Conversions of a DC Input
FIGURE 2. Histogram of 5000 Conversions of a DC Input
NOISE
The noise floor of the ADS8320 itself is extremely low, as
can be seen from Figures 1 and 2, and is much lower than
competing A/D converters. It was tested by applying a low
noise DC input and a 5.0V reference to the ADS8320 and
initiating 5000 conversions. The digital output of the A/D
0
1
0
1
at the Code Transition.
at the Code Center.
0
2
0
2
2510
3
72
3
Code
Code
2490
4864
4
4
0
5
64
5
0
6
0
6
9
converter will vary in output code due to the internal noise
of the ADS8320. This is true for all 16-bit SAR-type A/D
converters. Using a histogram to plot the output codes, the
distribution should appear bell-shaped with the peak of the
bell curve representing the nominal code for the input value.
The
68.3%, 95.5%, and 99.7%, respectively, of all codes. The
transition noise can be calculated by dividing the number of
codes measured by 6 and this will yield the 3 distribution
or 99.7% of all codes. Statistically, up to 3 codes could fall
outside the distribution when executing 1000 conversions.
The ADS8320, with < 3 output codes for the 3 distribu-
tion, will yield a < 0.5LSB transition noise. Remember, to
achieve this low noise performance, the peak-to-peak noise
of the input signal and reference must be < 50 V.
AVERAGING
The noise of the A/D converter can be compensated by
averaging the digital codes. By averaging conversion re-
sults, transition noise will be reduced by a factor of 1/ n,
where n is the number of averages. For example, averaging
4 conversion results will reduce the transition noise by 1/2
to 0.25 LSBs. Averaging should only be used for input
signals with frequencies near DC.
For AC signals, a digital filter can be used to low pass filter
and decimate the output codes. This works in a similar
manner to averaging; for every decimation by 2, the signal-
to-noise ratio will improve 3dB.
DIGITAL INTERFACE
SIGNAL LEVELS
The digital inputs of the ADS8320 can accommodate logic
levels up to 5.5V regardless of the value of V
ADS8320 can be powered at 3V and still accept inputs from
logic powered at 5V.
The CMOS digital output (D
V
input, then that IC may require more supply current than
normal and may have a slightly longer propagation delay.
CC
is 3V and this output is connected to a 5V CMOS logic
1 , 2 , and 3
distributions will represent the
OUT
ADS8320
) will swing 0V to V
CC
. Thus, the
CC
. If
®